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Can You Hear Me Now?

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Hair cells, the fingerlike projections in the inner ear that are so necessary for transmitting sound to the brain for processing and translation, have been regenerated in a mouse model, the first such restoration in an adult mammal. The finding, reported in the January 10 issue of Neuron by HMS researchers at Massachusetts Eye and Ear, holds potential for future therapies that may someday reverse deafness in humans.

Hearing loss affects nearly 50 million people in the United States. The most common form, sensorineural hearing loss, is caused by the loss of sensory hair cells in the cochlea or inner ear. Such loss can result from noise exposure, aging, infections, and certain antibiotics and anticancer drugs. Although hearing aids and cochlear implants can ameliorate the symptoms, there are no known treatments to restore hearing because auditory hair cells in mammals do not regenerate.

In the experiment, the researchers applied a drug to the cochleas of mice that had lost hearing owing to noise trauma. The drug, known for inhibiting an enzyme called gamma-secretase, had been selected for its ability to generate hair cells when added to stem cells isolated from the ear. When applied, the drug inhibited a signal generated by a protein called Notch on the surface of cells that surround hair cells. Once freed from Notch’s control, the supporting cells developed into new hair cells.